There are 4 kinds of fields (columns) that make up a table:
Control Fields are columns used to classify, index, sort and restrict the rows and/or columns in the table (e.g., geography, NAICS code, year, etc).
Data Fields are columns of data that are tabulated for industries, products, lines and other related data.
Data Quality Fields are columns that contain imputation rates, standard errors and other indicators of data quality for certain data fields.
Flag Fields are columns that are associated with each data field. When applicable, flag fields have symbols, or "flags," that replace data in the data fields. By default, flag fields are hidden in American FactFinder. Their values overlay or are appended to the data field values as appropriate and display only when downloading data.
Each table has descriptive text associated with it. Table notes have details about the table, including geographic coverage, data limitations and file size. To find the table notes, click on the "Table Notes" button to the top-right of the table.